1. Field of the Invention
The present invention relates to a device for measuring a imbalance of a disc-like object provided with a circular through-hole in the center thereof.
2. Description of the Prior Art
The imbalance of the disc-like object is generally expressed by first and second amounts. The first amount means an angular moment caused by the imbalance of the object when the object is rotated with its diameter as an axis, that is, a value of torque when torque becomes maximum according to a way of setting the diameter. The second amount means a direction in which a radius of those extending perpendicular to the diameter, by which the maximum torque is obtained, from the center of the object and present on the side lowered by the maximum torque extends from the center, and the value of second amount is expressed by the angle relative to a reference axis appropriately selected. In the following description, the first amount is shown as maximum torque value, the second amount as maximum torque direction, and the imbalance measuring of the object is performed by determinations of the maximum torque value and the direction.
Various devices for measuring the imbalance of disc-like object are well known. Typical of these conventional devices is a kind of static measuring device wherein the object is rotated slowly engaging with the force measuring means which can measure the change of force, and the changing amount of force added to the force measuring means due to the imbalance of the object is measured, and the imbalance of the object is calculated by the result of the measurements; and the stationarily measuring device shown in FIG. 1. The preceding measuring device was made complicated and large-sized and took a longer time in measurment because this device made it necessary to rotate the object. On the other hand, the stationary measuring device shown in FIG. 1 includes a base 50, a swing bearing 51 arranged to the base 50, a table 52 attached freely swingable to the swing bearing 51, and a rotary table 53 mounted freely rotatable on the table 52. One end portion of table 52 is supported by a load sensor 54 and a disc-like object 55 is mounted on the table 53. The object 55 is rotated and stopped together with the table 53 every predetermined angle. Signals supplied from the load sensor at every rotation stop are amplified by an amplifier 56. Amplified signals are operated by a computer 57 and the imbalance of the object thus obtained is displayed on a display means 57 a. It was necessary in this case that measurement be carried out at two angular positions of the table 53. Therefore, it took a longer time to measure. In addition, a precise bearing such as air bearing was needed to enhance measuring accuracy, thus making the cost of device high.